Process for the conversion of biomass to liquid fuels and specialty chemicals

ABSTRACT

The present invention relates to the conversion of solid biomass to liquid fuels and specialty chemicals. The process utilizes an activating step to make the biomass more susceptible to conversion, that is the biomass is broken down such that the components of the biomass are dissociated. Subsequently, the activated biomass undergoes a reaction to convert it to a bio-oil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the conversion of solid biomass toliquid fuels and specialty chemicals.

It has long been recognized that biomass, in particular biomass of plantorigin, is abundantly available and is a potential source of liquidfuels and valuable chemicals. See, for example, “Energy production frombiomass”, by P. Mc.Kendry—Bioresource Technology 83 (2002) p 37-46, and“Coordinated development of leading biomass pretreatment technologies”by C. E. Wyman et al, Bioresource Technology 96 (2005) 1959-1966.

Refined biomass materials, such as vegetable oils, starches, and sugars,can almost completely be converted to liquid fuels such as biodiesel(methyl or ethyl esters of fatty acids) and ethanol. However, the use ofthese refined biomass materials as starting points for liquid fuelsdiverts precious food resources from animal and even human consumption.This makes these starting materials expensive, and also meets withethical objections.

It is far more desirable to find a way for converting non-edible biomassto liquid fuels and valuable chemicals, in particular if this non-ediblebiomass does not at present have an economic use and is thereforeconsidered “waste”. Examples of such biomass materials includeagricultural wastes, such as bagasse, straw, corn stover corn husks andthe like. Other examples include forestry wastes, such as wood chips andsaw dust from logging operations or waste from paper and/or paper mills.What these materials have in common is that they contain significantamounts of lignocellulose and crystalline cellulose, making themresistant to chemical conversion and to fermentation. It is known thatthe biomass consists of three main components being lignin, amorphoushemi-cellulose and crystalline cellulose, assembled in such a compactmanner that makes it less accessible and therefore less susceptible tochemical and/or enzymatic conversion.

2. Description of the Related Art

Various processes have been proposed for converting non-edible biomassto liquid fuels, animal feeds, and chemicals. Generally speaking, theseprocesses fall into one of the following categories:

Hydrothermal Upgrading (Htu); See References

-   -   “Process for the production of liquid fuels from biomass” by Van        den Beld et al WO 02/20699 A1    -   “Developments in direct thermochemical liquefaction of biomass        1983-1990” by D. C. Elliott et al., Energy & Fuels 1991, 5,        399-410    -   “A literature survey of intermediate products formed during the        thermal aqueous degradation of cellulose” Polym. Plast.        Technology. Eng 11, (2), 127-157 (1978)

Pyrolysis; See Reference

-   -   “Pyrolysis of Wood/Biomass for Bio-Oil: A critical Review” by D.        Mohan et al., Energy & Fuels 2006, 20, p 848-889

Gasification (Followed by Fischer Tropsch Synthesis).

-   -   “Chemical Processing in High-pressure Aqueous        Environments—Development of Catalysts for Gassification”        by D. C. Elliott et al, Ind. Eng. Chem. Res. 1993, 32, 1542-1548

Acid Hydrolysis

-   -   Schmidt et al “Hydrolysis of biomass material” US2002/0117167A1

Enzymatic Fermentation.

See for instance reference: “A review of the production of ethanol fromsoftwood” by M. Galbe et al., Biomedical and Life Sciences, vol 59, no6,September 2002

Hydrothermal Upgrading (HTU) refers to processes whereby biomass isreacted with liquid water at elevated temperature (well above 200° C.)and pressure (50 bar or higher). The high temperatures and pressuresthat are needed to obtain suitable conversion rates make these processesexpensive, requiring special high pressure equipment constructed withspecial metal alloys which for commercial plants, are difficult tooperate and have relatively short life times. In addition, the productsobtained in HTU processes are heavily degraded because of polymerizationand coke formation that take place under the prevailing reactionconditions. The liquid products obtained by HTU processes tend to behighly acidic and corrosive, and unstable.

Pyrolysis generally refers to processes carried out at high temperatures(500 to 800° C.) in the absence of oxygen, or with so little oxygenpresent that little or no oxidation takes place. The resulting liquidproducts are of poor quality, heavily degraded, and low pH, and requireextensive (hydro-) treatment for upgrading to transportation fuels orchemical feedstocks.

It is desirable to develop a process for converting biomass under muchmilder conditions than prevail in the traditional HTU and pyrolysisprocesses, in part to avoid the high cost of equipment necessary foroperating under these conditions, and in part also to avoid the productdegradation taking place under these more severe reaction conditions.

Gasification of biomass, followed by FT synthesis, is inherentlyexpensive as it involves a complete breakdown of hydrocarbon material,followed by a synthesis of different hydrocarbons. This route involves acomplex multi-step and therefore costly processing scheme.

Any economic biomass conversion process must be aimed at preserving thechemical structures present in the biomass as much as possible, to theextent consistent with the goal of making liquid fuels. The overallscheme should be simple and low in capital as well as operating costs.

Enzymatic fermentation is capable of converting only a relatively smallportion of the available cellulose in biomass, generally on the order of40%. The process is slow, requiring 24 hours or more per batch andoperates best at low solid to liquid ratios. Accordingly, the processmust be carried out in large fermentation vessels. The enzymes used inthese processes are expensive when compared to the cost of chemicalsused in chemical conversion processes.

Acid hydrolysis has been proposed as a precursor to enzymaticfermentation. The purpose is to provide an initial breakdown of(ligno-)cellulose, so that more of it is available for subsequentfermentation. Acid hydrolysis is carried out under atmosphericconditions and at temperatures below 100° C. The handling of largequantities of acid makes this process unattractive, in particularbecause the acid must be either removed or neutralized before thefermentation step. The formed salts adversely affect the subsequentfermentation process.

There is a need for a low-cost process that is able to convert a largeproportion of the (ligno-)cellulosic material present in non-ediblebiomass under conditions that are mild enough to avoid high equipmentand energy costs and/or substantial degradation of the conversionproducts.

Biomass in general represents a composite comprising mainly lignin,amorphous hemi-cellulose and crystalline cellulose, which are assembledin a strong compact form, which due to the lack of accessibility isresistant to chemical treatments, impregnation, and dissolution. It ishighly desirable to develop means to dissociate these three maincomponents from the composite and develop susceptibility which willallow chemical reactions and subsequent conversions to take place. Ourinvention provides means to accomplish this by using a two step process:a) Breaking down/dissociation of the components within the composite anddeveloping susceptibility. b) Reacting the individual componentsappropriately using physical, mechanical, thermal and chemical means forthe efficient conversion to fuels and chemicals.

SUMMARY OF THE INVENTION

The present invention relates to a process for converting biomass to aliquid fuel comprising the steps of:

-   -   a) activating the biomass to make it more susceptible to        conversion;    -   b) optionally, adding a solvent;    -   c) partially converting the activated biomass to form a mixture        of solubilized material and unconverted biomass;    -   d) subjecting unconverted biomass from step c) to a conversion        process.

Due to the activation taking place in step a), optionally aided by theaddition of a solvent (step b), step c) can be carried out under mildconditions. As a result the product obtained in step c) is notsubstantially degraded. Unconverted biomass from step c) is subsequentlysubjected to a second conversion in step d). Optionally, and preferably,converted biomass obtained in step c) is removed from the unconvertedbiomass before the latter is subjected to a second conversion in stepd). If conversion products from step c) are first removed, step d) maybe carried out under more severe conditions than step c). In thealternative, step d) may be preceded by a second activation step so thatthe unconverted biomass is more susceptible to the conversion process ofstep d).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of the process of thepresent invention.

FIG. 2 is a schematic diagram of an alternate embodiment of the processof the present invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following is a description of certain embodiments of the invention,given by way of example only.

The present invention relates to a process for converting biomass to aliquid fuel comprising the steps of:

-   -   a) activating the biomass to make it more susceptible to        conversion;    -   b) optionally, adding a solvent;    -   c) partially converting the activated biomass to form a mixture        of solubilized material and unconverted biomass;    -   d) subjecting unconverted biomass from step c) to a conversion        process.

The process provides the general advantage of requiring less severeprocess conditions than, for example, traditional HTU or pyrolysisprocesses. Accordingly, the process is more cost-effective and requiressimpler less expensive equipment. The process is also environmentallymore acceptable, and produces product of higher quality, and moresuitable for conversion to fuels and chemicals.

Particular embodiments of the process provide homogenous, intimatemixtures of biomass material with a solvent and/or a solid and/or aliquid additive, which provides advantages for subsequent conversion.

In a preferred embodiment the biomass material is sensitized. Becausethe sensitized material has an increased susceptibility to hydrothermalconversion, the hydrothermal conversion itself may be carried out at alower temperature and pressure than is normally employed for this typeof reaction.

There are various ways in which the carbon based energy carrier materialmay be sensitized prior to the hydrothermal conversion step itself.

One process involves providing particles of the carbon based energycarrier material, and coating these particles with smaller particles ofa catalytic material. The coated particles are subjected to thermaltreatment, during which the energy carrier material becomes sensitized.This process is disclosed in detail in our co-pending patent applicationentitled “Pretreatment of particulate carbon-based energy carriermaterial” the disclosures of which are incorporated herein by reference.

Another process for sensitizing the carbon based energy carrier materialis suitable for energy carrier materials that contain a polymer ofphotosynthetic origin. In this process, small particles of an inorganicmaterial are embedded within the polymeric material of photosyntheticorigin. This process is disclosed in detail in our co-pending patentapplication entitled “Method of making a polymeric material ofphotosynthetic origin comprising particulate inorganic material” thedisclosures of which are incorporated herein by reference

Yet another process for sensitizing the carbon based energy carriermaterial comprises the step of contacting the carbon based energycarrier material with reaction products obtained in step b) of theprocess of the present invention. It will be understood that when theprocess is started no reaction product is yet available. Therefore, atthis stage, the carbon based energy carrier material may be sensitizedby some other method. It is also possible to start the reaction withnon-sensitized material, and carry out the hydrothermal conversion stepunder conventional conditions of temperature and pressure.

For example, the reaction may be started at a temperature of up to 370degrees centigrade, and a pressure of about 200 bar, or preferably withsuperheated steam (“dry steam”), producing a reaction product that ispractically suitable for mixing with the carbon based energy carriermaterial for sensitization purposes. Once enough reaction product isformed to operate the reaction with a continuous supply of sensitizedmaterial, the hydrothermal conversion conditions can then be changed toa temperature of less than 300 degrees centigrade and A pressure of lessthan 50 bar.

In a further preferred embodiment the sensitizing step a) comprises thestep of subjecting the energy carrier material to a pH swing of at least4 pH units. In one embodiment, the pH swing is produced by firstexposing the carbon-based energy carrier material to a pH of less than6, and increasing the pH to more than 8, with the proviso that the pHchange be at least 4 pH units. For example, if the acidic pH is 6, thepH is increased to at least 10; if the acidic pH is 5, the pH isincreased to at least 9; etc.

In an alternate embodiment the pH swing is produced by first exposingthe carbon-based energy carrier material to a pH of more than 8, andlowering the pH to less than 6, with the proviso that the pH change beat least 4 units. For example, if the alkaline pH is 8, the pH islowered to 4 or less; if the alkaline pH is 9, the pH is lowered to 5 orless; etc.

In a particularly preferred embodiment the pH swing comprises the stepsof first exposing the carbon-based energy carrier material to a pH ofless than 3, and increasing the pH to more than 6.

Conveniently the pH swing is produced by respective additions to thecarbon-based energy carrier material of an aqueous solution of an acidor a base. Suitable acids include mineral acids, in particular strongmineral acids such as such as hydrochloric acid, nitric acid, andsulfuric acid. Organic acids are also suitable, in particular organicacids as may be produced in the subsequent hydrothermal conversion ofthe energy carrier material, because of their abundant availability atthe site where the process is carried out, and their compatibility withthe other steps of the process.

Suitable bases include inorganic materials, in particular inexpensiveinorganic materials such as potash, soda ash, caustic, and lime.

The subsequent additions of an acid and a base (or a base and an acid)to the energy carrier material results in the presence of a salt. Hence,in a preferred embodiment, additive(s) added in the sensitizing step a)react to form a new crystalline phase. In general the salt does notinterfere with the subsequent, hydrothermal conversion reaction. Thehydrothermal conversion typically results in the formation liquidproduct comprising a water-rich phase and a hydrocarbon-rich phase, withvirtually all of the salt present in the water-rich phase. The salt maybe recovered from the water-rich phase by any suitable technique.

In a preferred embodiment the salt is embedded in the carbon-basedenergy carrier material in the form of small crystals. This is done bychanging the conditions such that salt present in solution precipitates.In general, it is undesirable to deposit salt crystals on the outersurface of the particles of energy carrier material. Therefore, excessliquid is drained off first, leaving the energy carrier material soakedwith a salt solution. Next, the conditions are changed to causeprecipitation of the salt within the particles of energy carriermaterial. This change of conditions may be anything that causesprecipitation of the specific salt, and may include, for example, achange in temperature, a change in pH, evaporation of the solvent(which, in most cases, is water), and combinations of such measures.

The salt crystals embedded within the particles of energy carriermaterial tend to break up or open up these particles, therebycontributing to the required sensitization of the energy carriermaterial to a subsequent hydrothermal treatment.

In an alternate embodiment the biomass is pretreated as follows in aprocess comprising the steps of:

-   a) providing the biomass material in particulate form;-   b) preparing a slurry of the particulate biomass material and a    solvent;-   c) introducing into the slurry a particulate, insoluble inorganic    material;

Suitably the source of the polymeric material is a form of agriculturalor forestry waste. Examples include bagasse, sugar beet pulp, choppedstraw, cotton linters, corn stalks, corn cobs, wood chips, saw dust,tree bark, grasses, and the like.

For the process of the invention the polymeric material is provided inparticulate form, preferably having a mean particle diameter of lessthan 3 mm, preferably in the range of from 0.1 to 1 mm. In general thisparticulate material is prepared from larger particles by techniquessuch as milling, grinding, pulverization, and the like. However, it hasbeen found that the process of the present invention is suitable for usewith relatively coarse particulate polymeric material, so that thisparticle size reduction step may be omitted. For example, wood chips asare produced when trees are cut with a chain saw may be used in thisprocess without further particle size reduction.

The particulate polymeric material is mixed with a solvent to form aslurry. Mixing may be carried out with any suitable mixer, such as ahelical mixer, an impeller, a screw mixer, and the like. It may bedesirable to employ a form of high shear mixing.

As it is desirable to operate at a low cost, in many cases water is apreferred solvent. However, other solvents may be available at low costfrom other stages of the conversion process. For example, if the processof the present invention is integrated with a fermentation process,ethanol may be abundantly available at low cost. Also, the reactionproduct of the process of the present invention comprises a liquidphase, which can be separated into an aqueous phase and an organicphase. The aqueous phase comprises water and water-soluble organiccompounds. This aqueous phase can be used as the solvent for making theslurry of step b), with or without prior removal of organic compoundscontained therein.

Generally, the inorganic material is selected from the group consistingof cationic clays, anionic clays, natural clays, hydrotalcite-likematerials, layered materials, ores, minerals, metal oxides, hydroxidesof metals of the alkaline and alkaline earth groups, and mixturesthereof. The insoluble inorganic material, which is introduced into theslurry in step c), is preferably an alkaline material. Even morepreferred are layered materials, or heat treated forms of layeredmaterials.

The layered material is selected from the group consisting of smectites,anionic clays, layered hydroxy salts, and mixtures thereof. Highlypreferred are Mg—Al and Ca—Al anionic clay.

Thermally treated layered materials are layered materials selected fromthe above group which have been thermally treated at a temperature inthe range of about 300-900° C.

The particles containing the (thermally treated) layered material mayadditionally comprise other materials. Examples of such other materialsare conventional catalyst components such as silica, alumina,aluminosilicates, zirconia, titania, boria, kaolin, acid leached kaolin,dealuminated kaolin, bentonite, (modified or doped) aluminum phosphates,zeolites (e.g. zeolite X, Y, REY, USY, RE-USY, or ZSM-5, zeolite beta,silicalites), phosphates (e.g. meta or pyro phosphates), sorbents,fillers, and combinations thereof.

Preferably, the particles also contain metals like W, Mo, Ni, Co, Fe, V,and/or Ce. Such metals may introduce a hydrotreating function into theparticles (especially W. Mo, Ni, Co, and Fe) or enhance the removal ofsulfur- and/or nitrogen-containing species (Zn, Ce, V).

The particles may be a spent (resid) FCC catalyst containing the(thermally treated) layered material. This would be very advantageous,as it involves the re-use of waste material. The spent catalyst may beground of pulverized into smaller particles, thereby increasing theirdispersibility.

The solid particles containing the (thermally treated) layered materialpreferably have a high accessibility, thereby being less vulnerable toblockage during the process.

The particulate inorganic material suitably has a mean particle diameterin the range of from 1 to 500 micrometers, preferably from 10 to 150micrometers.

Following are examples of specific layered materials suitable for use inthe present process.

Smectite

Smectites are the 2:1 clay minerals that carry a lattice charge andcharacteristically expand when solvated with water and alcohols. Thelayers are negatively charged. Between the layers, cations are hosted.Examples of smectites are montmorillonite and saponite, which are Mg—,Al—, and Si-containing smectites.

Naturally occurring or synthetically prepared smectites can be used. Amethod for preparing Mg—, Al—, and Si-containing smectites is disclosedin WO 01/12319. Thermal treatment, e.g. calcination at temperatures inthe range 300-900° C., leads to the formation of activated smectiteclays.

Anionic Clay

Anionic clays are layered structures corresponding to the generalformula[M_(m) ²⁺M_(n) ³⁺(OH)_(2m+2n).](X_(n/z) ^(z−)).bH₂Owherein M²⁺ is a divalent metal, M³⁺ is a trivalent metal, m and n havea value such that m/n=1 to 10, preferably 1 to 6, and b has a value inthe range of from 0 to 10, generally a value of 2 to 6, and often avalue of about 4. X is an anion with valance z, such as CO₃ ²⁻, OH⁻, orany other anion normally present in the interlayers of anionic clays. Itis more preferred that m/n should have a value of 2 to 4, moreparticularly a value close to 3.

In the prior art, anionic clays are also referred to as layered doublehydroxides and hydrotalcite-like materials.

Anionic clays have a crystal structure consisting of positively chargedlayers built up of specific combinations of metal hydroxides betweenwhich there are anions and water molecules. Hydrotalcite is an exampleof a naturally occurring anionic clay in which Al is the trivalentmetal, Mg is the divalent metal, and carbonate is the predominant anionpresent. Meixnerite is an anionic clay in which Al is the trivalentmetal, Mg is the divalent metal, and hydroxyl is the predominant anionpresent.

In hydrotalcite-like anionic clays the brucite-like main layers arebuilt up of octahedra alternating with interlayers in which watermolecules and anions, more particularly carbonate ions, are distributed.The interlayers may contain anions such as NO₃ ⁻, OH, Cl⁻, Br⁻, I⁻, SO₄²⁻, SiO₃ ²⁻, CrO₄ ²⁻, BO₃ ²⁻, MnO₄ ⁻, HGaO₃ ²⁻, HVO₄ ²⁻, ClO₄ ⁻, BO₃ ²⁻,pillaring anions such as V₁₀O₂₈ ⁶⁻ and Mo₇O₂₄ ⁶⁻, monocarboxylates suchas acetate, dicarboxylates such as oxalate, alkyl sulfonates such aslauryl sulfonate.

Upon thermal treatment at a temperature above about 200° C., anionicclays are transformed into so-called solid solutions, i.e. mixed oxidesthat are re-hydratable to anionic clays. At higher temperatures, aboveabout 800° C., spinel-type structures are formed. These are notre-hydratable to anionic clays.

The thermally treated anionic clay that can be present in the solidparticles to be used in the process of the present invention can be asolid solution or a spinel-type material.

For the purpose of the present invention various types of (thermallytreated) anionic clays are suitable. Examples of suitable trivalentmetals (M³⁺) present in the (thermally treated) anionic clay includeAl³⁺, Ga³⁺, In³⁺, Bi³⁺, Fe³⁺, Cr³⁺, Co³⁺, Sc³⁺, La³⁺, Ce³⁺ andcombinations thereof. Suitable divalent metals (M²⁺) include Mg²⁺, Ca²⁺,Ba²⁺, Zn²⁺, Mn²⁺, Co²⁺, Mo²⁺, Ni²⁺, Fe²⁺, Sr²⁺, Cu²⁺, and combinationsthereof. Especially preferred anionic clays are Mg—Al and Ca—Al anionicclays.

Suitable anionic clays can be prepared by any known process. Examplesare the co-precipitation of soluble divalent and trivalent metal saltsand slurry reactions between water-insoluble divalent and trivalentmetal compounds, e.g. oxides, hydroxides, carbonates, andhydroxycarbonates. The latter method provides a cheap route to anionicclays.

Layered Hydroxy Salts

Metal hydroxy salts (LHS) are distinguished from anionic clays in thatthey are built up of divalent metals only, whereas layered doublehydroxides are built up of both a divalent and a trivalent metal.

An example of a LHS is a hydroxy salt of a divalent metal according tothe following idealized formula: [(Me²⁺, M²⁺)₂(OH)₃]⁺(X^(n−))_(1/n)],wherein Me²⁺ and M²⁺ may be the same or different divalent metal ionsand X^(n−) is an anion other than OH⁻. Another example of LHS has thegeneral formula [(Me²⁺, M²⁺)₅(OH)₈]²⁺(X^(n−))_(2/n)], wherein Me²⁺ andM²⁺ may be the same or different divalent metal ions and X is an anionother than OH⁻.

If the LHS contains two different metals, the ratio of the relativeamounts of the two metals may be close to 1. Alternatively, this ratiomay be much higher, meaning that one of the metals predominates over theother. It is important to appreciate that these formulae are ideal andthat in practice the overall structure will be maintained, althoughchemical analysis may indicate compositions not satisfying the idealformula.

Examples of suitable layered hydroxy salts with one type of metal areZn-LHS (e.g. Zn₅(OH)₈(X)₂, Zn₄(OH)₆X, Zn₅(OH)₆(X)₂.2H₂O, Zn₃(OH)₄(X)₂),Co-LHS (e.g. CO₂(OH)₃X, Ni-LHS (e.g. Ni₂(OH)₃X), Mg-LHS (e.g.Mg₂(OH)₃X), Fe-LHS, Mn-LHS, and La-LHS (La(OH)₂NO₃). Examples ofsuitable layered hydroxy salts comprising two or more different types ofmetals are Zn—Cu LHS, Zn—Ni LHS, Zn—Co LHS, Fe—Co LHS, Zn—Mn LHS, Zn—FeLHS, Ni—Cu LHS, Cu—Co LHS, Cu—Mg LHS, Cu—Mn LHS, Fe—Co LHS, Ni—Co LHS,Zn—Fe—Co LHS, Mg—Fe—Co LHS, and Ni—Cu—Co LHS. Especially preferredlayered hydroxy salts are Zn—Mn LHS and Zn—Fe LHS.

Examples of suitable interlayer anions X^(n−) are NO₃ ⁻, OH, Cl⁻, Br⁻,I⁻, SO₄ ²⁻, SiO₃ ²⁻, CrO₄ ²⁻, BO₃ ²⁻, MnO₄ ⁻, HGaO₃ ²⁻, HVO₄ ²⁻, ClO₄ ⁻,BO₃ ²⁻, pillaring anions such as V₁₀O₂₈ ⁶⁻ and Mo₇O₂₄ ⁶⁻,monocarboxylates such as acetate, dicarboxylates such as oxalate, alkylsulfonates such as lauryl sulfonate.

LHS exchanged with (bi)carbonates or organic anions provides theadvantage that upon calcination, the anion will decompose, therebyincreasing the porosity and surface area of the LHS.

Suitable methods for the preparation of layered hydroxy salts involvethe reaction of a metal oxide with a dissolved metal salt (see Inorg.Chem. 32 (1993) 1209-1215) and co-precipitation from metal saltsolutions (see J. Solid State Chem. 148 (1999) 26-40 and J. Mater. Chem.1 (1991) 531-537). After preparation of the LHS, the interlayer anionsmay be exchanged, if so desired, by a regular ion-exchange procedure.

Upon thermal treatment of a LHS at a temperature above 300° C., metaloxides or mixed metal oxides are formed.

An alternate process involves the use of an extruder and/or a kneader.Kneading is very suitable to provide homogeneous and intimate mixing andallows for reactions to take place, while extrusion provides high shearmechanical treatment of the materials which aids the dissolution thebiomass composites and facilitates the transport of the materials. Inparticular the use of a screw extruder is preferred for use herein,because it allows for operation at high pressures without requiringexpensive equipment.

It will be understood that the mixing step may be combined with theprocess of reducing the particle size of the biomass material. Forexample, ball milling or grinding of the biomass in the presence of aparticulate solid material will result in an intimate mixture of thebiomass and the particulate solid material.

Focusing now on the use of an extruder and/or kneader for the purpose ofactivating the biomass, it is possible to operate the process atincreased temperature. Many screw extruders are provided with a heatingmantle through which steam or heated oil may be circulated. It is alsopossible to inject steam into nozzles provided in predeterminedlocations of the barrel. Steam injection provides a combined effect ofheating the biomass and adding a solvent (water).

The pressure inside the extruder is determined by the viscosity of themass within the extruder the design of the screw within the extruder(for example, a tapered pitch screw provides a higher pressure than aconstant pitch screw), and the design of the perforated plate at theoutlet of the extruder. The back pressure provided by this plate is afunction of the amount of open area in relation to the amount of closedarea, with lower open area/closed area ratios providing greater backpressure.

If a single pass through an extruder does not provide sufficient mixing,two or more extruders may be provided in series, or the material may besubjected to two or more passes through one extruder. Similarly, thecapacity of a plant may be readily increased by operating two or moreextruders in parallel.

Suitable solvents for use in step b) include water, alcohols (inparticular ethanol and glycerol), bio-oil or other products from thesubsequent conversion of the biomass, liquid acids, aqueous solutions ofacids and bases, liquid CO₂, and the like. Water is the preferredsolvent in most applications, because of its availability, low cost, andease of handling. Liquids that are produced during the subsequentconversion of the biomass are also readily available and may bepreferred for that reason.

Suitable solid materials for use in step a) include solid acids andbases, salts, minerals, clays, layered materials, and the like. Solidmaterials having catalytic properties are preferred. Examples includemetal oxides, metal hydroxides, alkaline and alkaline earth oxides,hydroxides, carbonates, hydroxylcarbonates, hydrotalcite-like materials,etc. As has been noted earlier, it may be desirable to add several solidmaterials to the biomass, or a combination of one or more solidmaterials and one or more solvents.

When kneading and/or grinding biomass with a solid inorganic particulatematerial it may be possible to form a co-crystal of a crystallizablecomponent of the biomass (e.g., cellulose) and the inorganic material.The formation of such a co-crystal may be confirmed by an XRD patternshowing a crystal structure that is different from that of the biomassstarting material and different also from the crystal structure ofinorganic material. (See reference: Chem. Commun, 2002 2372-2373,“Mechanochemistry and co-crystal formation: effect of solvent onreaction kinetics”, Ning Shank Fumio Toda and William Jones)

Similarly, it is possible to add precursors of inorganic solids, andcausing them to solidify or even crystallize during the mixing process.For example, certain inorganic solids may precipitate from solution inresponse to an increase in temperature or a change in pH. An increase intemperature may be effected in the kneader by heating the barrel, or byinjecting steam. A pH change may be effected by injecting a solution ofan acid or a base. Similarly, amorphous materials may be caused tocrystallize by increasing the temperature of the mixture.

As mentioned above, the addition of a solvent is optional. For example,in many cases water is the solvent of choice. Many forms of non-ediblebiomass contain sufficient quantities of water for the present purpose,obviating the need for adding additional solvent. It may even bedesirable to remove water during the activation step. This may forexample be accomplished by heating the biomass to a temperature above100° C., and letting off steam via pressure valves located along thebarrel of the extrude, if an extruder is used in the process.

In many cases conversion step c) commences while the activated biomassis still being processed in the kneader or extruder or in both. If thisprocess is not completed in the kneader, the activated biomass may beprocessed further in a second kneader, or it may be subjected to asecond pass through the first kneader. Alternatively, the biomass may betransferred to a different processor to complete step c). A suitableexample of such a processor is a filter press, which can be operated atdesirable conditions of temperature and pressure.

It is highly preferred that liquid products resulting from conversionstep c) be separated from unconverted biomass. The purpose of thisseparation is twofold. Firstly, it reduces the mass of material thatneeds to be subjected to further conversion in step d), which makes theoperation of step d) more efficient. Secondly, it avoids subjectingliquid conversion products from step c) to the subsequent conversionprocess, avoiding a degradation of this liquid product by such furtherprocessing. The separation may involve a filtration device, such as afilter press, a centrifuge, a membrane filter, or a nano-filter. Duringsuch separation solvent may be added, or heat and/or steam may be added.Also, the separation may be carried out under elevated pressure.

In a specific embodiment, part of the first conversion takes place in afilter press under conditions of increased temperature and pressure.This may be accomplished by loading the activated biomass into a filterpress, and injecting steam to increase both the temperature and thepressure. After this first conversion step is completed the filter pressis de-pressurized over a filter medium, such as a filter cloth orscreen, and the reaction product is separated into a liquid filtratestream and a filter cake. The liquid stream comprises solvent and liquidconversion product, as well as fine particles of unconverted biomass.The filter cake comprises unconverted biomass, retained solvent, andliquid reaction product.

As used herein, the term “unconverted biomass” refers to biomass thathas not been converted to a liquid product in step c). The term includesbiomass material that has not undergone any chemical conversion. Theterm also includes biomass that has undergone some conversion, butinsufficient to form a liquid. For example, cellulose may have beenconverted to cellulose of a lower average molecular weight, but still besolid. This would be considered “unconverted biomass” within the meaningof this term as used herein. Such a material may well be an “activatedunconverted biomass” if its molecular weight is reduced and/or its macroand/or micro structure has changed, in a way that makes it moresusceptible for conversion to a liquid product in step d).

In the alternative the liquid may be separated from remaining solids bynano-filtration or membrane separation. Instead of a filtrationtechnique an extractive separation may be used.

The unconverted biomass from step c) contains the component of thebiomass that is sometimes referred to as “recalcitrant cellulose”. Thisis the part of the cellulose that is not readily converted under mildconditions. Dependent on the biomass source, this recalcitrant cellulosemay be predominantly lignin, or crystalline cellulose, or both. Theunconverted biomass may be in a particulate form and the particles ofunconverted biomass contain particles of organic, or inorganic material,which can have catalytic properties.

The unconverted cellulose is subjected to a second conversion process instep d). If the liquid conversion product of step c) is removed from theunconverted biomass prior to step d), this second conversion may becarried out under more severe conditions than the first conversion,without risking degradation of reaction products already formed. Forexample, the unconverted biomass may be subjected to a conventional HTUor pyrolysis process. In one embodiment, the conversion process of stepd) may be selected from the group consisting of a hydrothermal process,a pyrolysis process, a flash pyrolysis process, a gasification process,a thermal cracking process, a catalytic cracking process, ahydrocracking process, an acid hydrolysis process, an enzymatic process,and aqueous reforming process and combinations thereof.

In a preferred embodiment of the process of the present invention, theunconverted biomass is activated prior to step d) so that step d) may becarried out under less severe conditions than the prior art HTU andpyrolysis processes. In many cases the unconverted biomass from step c)is already activated, for example because inorganic particulatematerials added in step a) are carried over with the unconverted biomassinto step d). The unconverted biomass may also be activated as a resultof a partial conversion in step c), insufficient to render the biomassliquid, but sufficient to make it more susceptible to furtherconversion.

Any conversion process is suitable for use in step d). HTU and pyrolysishave already been mentioned; desirably, these processes are conductedunder conditions as mild as the activation of the biomass will permit.Gasification may be a desirable option, for example to create gaseousfuel for meeting the heat requirements of the overall process. Preferredis a gasification process producing a synthesis gas, and wherein thesynthesis gas is subsequently converted into a liquid hydrocarbonmixture. In some cases the activated unconverted biomass may beconverted to ethanol by enzymatic fermentation.

In most cases, both steps c) and d) produce a mixture of liquid biomassderivative compounds, jointly referred to as “bio-oil”. This bio-oil maybe converted to suitable liquid transportation fuels in modifiedrefinery processes such as fluid catalytic cracking, hydroconversion,thermal conversion, and the like. In these processes the bio-oil may bethe sole feedstock, or it may be blended with conventional, crudeoil-based feedstocks, i.e. fossil fuels. It is preferred that thebio-oil be converted to a liquid,fuel suitable for use in an internalcombustion engine.

In another embodiment the activation step a) is conducted in akneader/extruder assembly in the presence of an inorganic solid, forexample an alkaline or alkaline earth metal oxide or hydroxide, and theproduct of step c) is hydrothermally treated in step d). The inorganicmaterial which is homogenously mixed in step a)/step b) is thus mosteffectively dispersed and present in steps c) and/or d) in intimatecontact with the unconverted biomass, resulting in an efficientconversion. Said solids may possess catalytic properties that furtherenhance the conversion process.

In another embodiment the inorganic additive introduced in step a) maybe simply a heat transferring medium, like for example sand, clay or amineral, ore or soil, which may have also catalytic properties. In thiscase the product of step c) can be subjected to a pyrolysis conversionprocess. The advantage of this process is that here the heat transfermedium is in close and intimate contact with the biomass in a dispersedform.

In another embodiment the activation in step a) may involve the additionof an acid or a base, which, aided by the application of heat and/orsteam, will break down the compact structure of the biomass composite,rendering it more susceptible to a subsequent conversion, for example byacid hydrolysis and/or enzymatic conversion.

In another embodiment the biomass in step a) containing water andoptionally an additive is heated above 100° C., while being mechanicallytreated, so that the water is allowed to evaporate.

In another embodiment, the biomass is mechanically processed in thepresence of other carbonaceous materials such as coal, lignite, tarsands and shale in step a) and step b) optionally with the addition ofadditives, followed by gasification of the unconverted materials.

In another embodiment shaped bodies produced in step a), b) and/or c)containing optionally an additive may be thermally treated to causefurther biomass dissolution and subsequently treated with enzymes.

In another embodiment shaped bodies produced in step a), b) and/or c)containing optionally an additive may be hydro-thermally treated tocause further biomass dissolution, and subsequently treated withenzymes.

In another embodiment the biomass is intimately mixed with an additivein a ball mill, grinding the components together to form the activatedbiomass. Optionally a liquid solvent can be added.

In another embodiment the biomass is grinded with an additive in afluidized and/or spouted bed. Optionally a liquid solvent can be added.

In another embodiment the unconverted biomass of step c), which in manycases appears to be the fibrous crystalline cellulose component of thebiomass coated with an additive, is converted to paraffins suitable fordiesel fuels.

In another embodiment the fibrous crystalline cellulose coated with ancatalytically active additive is converted to diesel, according to orsimilar to the reactions scheme as suggested by Huber et al., see: G. W.Huber, J. N. Chheda, C. J. Barrett, J. A. Dumesic, Science 308 (2005)1446.

In another embodiment the unconverted biomass of step c), which oftenappears to be the fibrous crystalline cellulose coated with an additive,is converted to materials suitable for paper, paper products,nano-composites, cardboard, building materials, board or constructionmaterials.

In another embodiment the unconverted material (mainly crystallinecellulose) is converted to a transportation fuel by aqueous phasereforming as suggested by Huber et al., see: G. W. Huber, J. N. Chheda,C. J. Barrett, J. A. Dumesic, Science 308 (2005) 1446. In yet anotherembodiment, the unconverted biomass is converted to electrical energy.

In another embodiment the solubilized material is converted to atransportation fuel by aqueous phase reforming as suggested by Huber etal., see: G. W. Huber, J. N. Chheda, C. J. Barrett, J. A. Dumesic,Science 308 (2005)1446.

In another embodiment the unconverted material of step b and/or c) isfirst submitted to electromagnetic and/or ultrasound energy, optionallyin the presence of a polar solvent such as ethanol. Following thistreatment the so activated material is converted by any of the abovemeans.

In another embodiment the unconverted material of step b and/or c),which comprises a material susceptible to the absorption ofelectro-magnetic radiation is first submitted to electromagneticoptionally in the presence of a polar solvent such as ethanol. Followingthis treatment the so activated material is converted by any of theabove means.

In another embodiment the unconverted material of step b and/or c) isfirst submitted to intimate mixing with an additive, optionally in thepresence of a solvent such as ethanol. Following this treatment the soactivated material is converted by any of the above means.

Thus, the invention has been described by reference to certainembodiments discussed above. It will be recognized that theseembodiments are susceptible to various modifications and alternativeforms well known to those of skill in the art.

EXAMPLE 1

Saw dust was prepared by repeatedly sawing through a piece ofconstruction lumber with a circular saw. Judged by appearance the sawdust particles were predominantly rod-like in shape, and had a meanaverage larger particle dimension of about 1-2 mm, and a smallerparticle dimension of about 0.5 mm.

Experiments were carried out in 2 mL glass test tubes, able to withstandpressures well in excess of 10 bar. The test tubes were provided withbakelite stoppers, which were equipped with pressure gauges formonitoring the pressure inside the test tubes. The test tubes wereprovided with magnetic stirrers, and heated in an oil bath. In allexperiments the oil bath was kept at 180° C. The pressure inside thetest tubes was 10 bar, corresponding with a temperature inside the tubesof 180° C.

Hydrotalcite (“HTC”) from Aldrich, which is magnesium aluminumhydroxycarbonate of the formula Mg₆Al₂(CO₃)(OH)₁₆. 4H2O, CAS number11097-59-9, was calcined in air for 1 hour at 650° C.

In one of the 2 mL test tubes were weighed 90 mg of saw dust, 21 mg ofthe calcined HTC, and 1390 mg distilled H₂O. The mixture was heated at180° C. under stirring for 1 hour (sample B1).

In a comparative example a separate sample of saw dust from the samesource was heated in distilled water, under stirring, for 1 hour at 180°C., in the absence of HTC or any other additives (sample A2).

In a second example according to the invention an uncalcined sample (21g) of HTC was slurried with 89 mg saw dust and 1440 mg distilled water,and heated under stirring at 180° C. for 1 hour (sample B2).

The treated saw dust samples were judged visually for the percentage ofliquefaction, and compared under an optical microscope with a virgin sawdust sample (sample A1)

The results are compiled in the following table:

Sample % liquefaction Observation A1   0% Reference A2 <10% Noobservable changes; structure of fibers and cells as in sample A1 B1About 40% Wood cells have disappeared; only here and there isolated celldebris still visible B2 >10%, <40% HTC particles apparently hydrophobic;effect less pronounced than in B1; some cell material had beendestroyed, but intact cells still present.

The results indicate that the hemicellulose and lignin components of thesaw dust particles were fully liquefied in experiment B1, but that mostof the crystalline cellulose had remained solid. The uncalcinedhydrotalcite sample (experiment B2) was apparently hydrophobic. Theparticles may have been coated with an organic material, such as stearicacid, which is often done to make the particles compatible withsynthetic polymeric materials. Calcination made the hydrotalcite moreeffective because the material was hydrophilic after calcination. Inaddition, calcination is known to make layered materials such as HTCmore catalytically active.

The experiments are repeated with particles of kaolin, bentonite,montmorillonite, Zn-LHS, and ZnO/FeO mixed metal oxide, respectively.Similar results are obtained.

EXAMPLE 2

Biomass material made from White Pine wood milled to an average particlesize of 500 micrometers is dispersed in a solution containing Mg(NO₃)₂and Al(NO₃)₃. The Mg/Al mole ratio for this solution is 3. The resultingslurry is stirred for thirty minutes to allow maximum penetration of thesolution into the wood particles. The excess solution is drained off andthe resulting wet biomass material re-slurried in sodium hydroxidesolution such that the final pH is 9 to 10.

The resulting slurry is divided into two portions. The first portion isaged at 85° C. for six hours. The second portion is aged at 180° C. forone hour.

The resulting slurries are filtered and dried.

The presence of a mixture crystalline cellulose and HTC is confirmed byX-ray diffraction in both samples with the higher temperature treatmentshowing higher crystallinity.

Thermal decomposition of these samples is performed using aMettler-Toledo TGA/SDTA851e thermo balance. The samples (10-15 mg) areplaced into alumina cup (70 ml) and heated from 25 to 700° C. at aheating rate 5° C. min⁻¹ under Ar (Argon) flow (30 ml/min).

DTG curves are calculated from the corresponding weight versustemperature curve. Total weight loss is determined as the differencebetween initial (at 25° C.) and remaining weight (at 600° C.) of thesample. In the case of biomaterial-catalyst mixture total weight loss isdetermined by subtracting the amount of catalyst from the initial andremaining weight assuming that catalyst does not change during theexperiment.

The weight loss for the two samples containing in-situ HTC are about 5to 10% higher than the untreated wood, while the decomposition of thesewood samples starts at a lower temperature than the untreated wood.

EXAMPLE 3

White Pine wood chips are initially pulverized with a mechanical mixerfor 5 min to reduce the particle size to about 5 mm. This wood materialis wet milled (15 wt % slurry based on weight of wood) along with rawnatural magnesite powder (wood to magnesite ratio of 10:2) in aplanetary high energy mill (Puverisette 6) for three hours. The slurryis dried at 100° C.

The presence of the inorganic phase, MgCO₃ along with cellulose isconfirmed by X-ray diffraction.

Using the same method described in Example 2 above, the weight loss forthe dried wood sample treated with magnesite is about 5 to 10% higherthan the untreated wood, while the decomposition of the wood starts at alower temperature than the untreated wood.

EXAMPLE 4

Repeat Example 3 replacing magnesite powder with MgCl₂ solution (wood toMgCl₂ ratio of 10:2). The final slurry is 15% solids based on the weightof the wood.

The presence of the inorganic phase along with cellulose is confirmed byX-ray diffraction.

Using the same method described in Example 2 above, the weight loss forthe dried wood sample treated with MgCl₂ is about 5 to 10% higher thanthe untreated wood, while the decomposition of the wood starts at alower temperature than the untreated wood.

EXAMPLE 5

A small amount of water (2% based on the weight of the wood) is added toa mixture of biomass material of White Pine wood (average particle sizeof 500 millimicrons) and magnesite powder is milled in a planetary highenergy mill (Pulverisette 6) for three hours.

The presence of the inorganic phase, MgCO₃ along with cellulose isconfirmed by X-ray diffraction.

Using the same method described in Example 2 above, the weight loss forthe dried wood sample treated with magnesite is about 5 to 10% higherthan the untreated wood, while the decomposition of the wood starts at alower temperature than the untreated wood.

EXAMPLE 6

Repeat Example 5, where the water is replaced by ethanol.

The presence of the inorganic phase, MgCO₃ along with cellulose isconfirmed by x-ray diffraction.

Using the same method described in Example 2 above, the weight loss forthe dried wood sample treated with magnesite is about 5 to 10% higherthan the untreated wood, while the decomposition of the wood starts at alower temperature than the untreated wood.

1. A process for converting biomass to a bio-oil comprising the stepsof: a) adding one or more additives that act to subject the biomass to apH swing of at least 4 pH units to activate the biomass in order toproduce an activated biomass that is more susceptible to conversion; b)optionally adding a solvent to said activated biomass; c) partiallyconverting the activated biomass to form a first bio-oil and leave anunconverted biomass; and d) subjecting the unconverted biomass from stepc) to a conversion process to produce a second bio-oil.
 2. The processof claim 1 wherein the biomass in step a) is in particulate form, and atleast two additives are added in step a) wherein at least a potion ofthe at least two additives react to form a crystalline phase distributedwithin the biomass particle.
 3. The process of claim 2 wherein thebiomass comprises at least one compound selected from the groupconsisting of cellulose and lignin.
 4. The process of claim 3 whereinthe cellulose comprises crystalline cellulose.
 5. The process of claim 1comprising, after step c) and before step d), the additional step ofseparating unconverted biomass from the first bio-oil.
 6. The process ofclaim 5 wherein the unconverted biomass in step d) comprises crystallinecellulose.
 7. The process of claim 6 wherein one or more additives areadded to the unconverted biomass from step c) wherein such additivesactivate the biomass to make it more susceptible to conversion prior tostep d).
 8. A process for converting biomass to a bio-oil comprising thesteps of: a) adding an inorganic material, and optionally a solvent, tothe biomass to form a mixture wherein said inorganic material isselected from the group consisting of cationic clays, anionic clays,natural clays, hydrotalcite materials, layered materials, minerals,metal oxides, hydroxides of metals of the alkaline and alkaline earthgroups, and mixtures thereof and wherein the inorganic material is in aparticulate form; b) treating said mixture in a mechanical device tocause a homogeneous and intimate mixing of its components; c) partiallyconverting the biomass in said mixture during the treating of step b) toproduce a first bio-oil and leave an unconverted biomass; and d)subjecting the unconverted biomass from step c) to a conversion processto produce a second bio-oil.
 9. The process of claim 8 wherein themechanical devise is an extruder which extrudes the mixture to producean extrudate and during the extrusion additional additives are added andheat and/or steam is added to the extruding mixture and furthercomprising drying, steaming and/or calcining the extrudate from theextrusion prior to step d).
 10. The process of claim 8 wherein theconversion process of step d) is selected from the group consisting of ahydrothermal process, a pyrolysis process, and a flash pyrolysisprocess, a gasification process, a thermal cracking process, a catalyticcracking process, a hydrocracking process, an acid hydrolysis process,an enzymatic process, and aqueous reforming process and combinationsthereof.
 11. The process of claim 8 wherein the process furthercomprises the additional steps of (i) converting the second bio-oil to aliquid fuel, suitable for use in an internal combustion engine and (ii)converting the first bio-oil obtained in step c) to a liquid fuel,suitable for use in an internal combustion engine and wherein theadditional steps (i) and (ii) comprise conversion in a unit selectedfrom an FCC unit, a Hydrocracking unit, a Hydrotreating unit, a ThermalCracking unit, and combinations thereof.
 12. The process of claim 8wherein the first bio-oil and the second bio-oil are blended with fossilfuels prior to processing in a refinery.
 13. The process of claim 8wherein the first bio-oil is subsequently converted to a transportationfuel by aqueous phase reforming.
 14. The process of claim 8 wherein,prior to step d), the unconverted biomass from step c) is submitted tointimate mixing with an additive, optionally in the presence of asolvent.
 15. The process of claim 8 wherein prior to step a) one or moreadditives are added to the biomass wherein such additives activate thebiomass so that it is more susceptible to conversion.
 16. The process ofclaim 15 wherein the one or more additives act to subject the biomass toa pH swing of at least 4 pH units.
 17. The process of claim 16 whereinthe biomass is in particulate form prior to step a). and the one or moreadditives are at least two additives wherein at least a potion of the atleast two additives react to form a crystalline phase distributed withinthe biomass particle.
 18. The process of claim 8 comprising, after stepc) and before step d), the additional step of separating the unconvertedbiomass from the first bio-oil.
 19. The process of claim 18 wherein thebiomass comprises lignin, hemi-cellulose and crystalline cellulose andwherein in step c) at least part of the hemi-cellulose is converted tothe first bio-oil such that the unconverted biomass comprises mainlylignin and crystalline cellulose.
 20. The process of claim 19 whereinprior to step d) one or more additives are added to the unconvertedbiomass from step c) such that the unconverted biomass is activated tomake it more susceptible to conversion prior to step d).